The common rail type fuel injection apparatus, superior in controllability to the mechanical fuel injection pump-nozzle system, has been previously proposed as a fuel supply system for multi-cylinder diesel engines and the like (e.g., see Japanese Patent Application Laid-Open Publication No. 2000-18052).
This type of fuel injection apparatus stores fuel, pressurized to a given pressure by a high-pressure pump, in a common rail and injects fuel stored in the common rail from a given injector in synchronization with fuel injection timings. A controller is provided to control the common rail fuel pressure and the operations of the individual injectors such that fuel is injected in optimal fuel injection conditions for the engine operation status.
Thus, the common rail type fuel injection apparatus has hitherto been developed as a fuel injection apparatus with excellent controllability because the apparatus is capable of controlling, in addition to the fuel injection amount and time, the fuel injection pressure—the pressure determined by the common rail fuel pressure—according to the engine operation status.
A description will be given below of a fuel injection system equipped with an ordinary common rail type fuel injection apparatus.
FIG. 17 is a schematic view of the overall configuration of a fuel supply system in a multi-cylinder diesel engine equipped with a common rail type fuel injection apparatus. The present common rail type fuel injection apparatus comprises a plurality of fuel injection valves (hereinafter referred to as “injectors”) b, b, . . . attached correspondingly to individual cylinders of the diesel engine (hereinafter simply referred to as “engine”) a, a common rail c for accumulating high-pressure fuel under a relatively high pressure (common rail pressure: 20 MPa, etc.), a high-pressure pump f for pressurizing fuel, sucked from a fuel tank d via a low-pressure pump e, to a high pressure and injecting the fuel into the common rail c and a controller (ECU) g for electronically controlling the injectors b, b, . . . and the high-pressure pump f.
Each of the injectors b, b, . . . is attached to the downstream end of each of fuel pipes that individually communicate with the common rail c. Fuel injection from the injectors b is controlled, for example, by energizing and de-energizing (ON/OFF) injection control solenoid valves h provided midway along the fuel pipes. That is, the injectors b inject high-pressure fuel supplied from the common rail c to the combustion chamber of the engine a during the time period when the injection control solenoid valves h are open. For this reason, a given high common rail pressure (20 MPa), equivalent to the fuel injection pressure, must be accumulated in the common rail, as a result of which the high-pressure pump f is connected via a fuel supply pipe i and a discharge valve j.
On the other hand, the ECUg receives engine information inputs such as engine rpm and load and outputs a control signal to the injection control solenoid valves h so as to obtain the fuel injection time and amount judged optimal based on these signals. At the same time, the ECUg outputs a control signal to the high-pressure pump f so as to provide the optimal fuel injection pressure in accordance with the engine rpm and load. Further, the common rail c is provided with a pressure sensor k for detecting the common rail inner pressure, and the fuel injection amount discharged from the high-pressure pump f to the common rail c is controlled such that the signal from the pressure sensor k becomes the preset optimal value in accordance with the engine rpm and load.
As disclosures of methods of detecting the common rail fuel pressure, a fuel injection apparatus disclosed in Japanese Patent Application Publication No. 7-122422 and a common rail pressure detector disclosed in Japanese Patent Publication No. 3235201 are proposed.
Japanese Patent Application Publication No. 7-122422 discloses constant monitoring of the common rail fuel pressure, whereas Japanese Patent Publication No. 3235201 discloses computation of the common rail fuel pressure without directly detecting the pressure.
Incidentally, to obtain the optimal fuel injection conditions (fuel injection time and amount) appropriate for the engine rpm, load and so forth in such a common rail type fuel injection apparatus, it is necessary to recognize with high accuracy the common rail fuel pressure—the pressure governing the fuel injection pressure—and exercise control such that the optimal pressure is constantly maintained as the common rail fuel pressure. That is, it is essential to recognize the common rail fuel pressure with high accuracy, thus allowing proper drive control of the high-pressure pump and fuel injection control associated therewith.
As for the common rail type fuel injection apparatus previously proposed, however, proper proposals have yet to be made at present as to collection of fuel pressure data in the common rail and further as to improvement of the data accuracy.
In light of the above, it is an object of the present invention to improve the accuracy of fuel pressure detection data in the common rail in a common rail type fuel injection apparatus and thereby improve the reliability of basic data used for engine control and other purposes.